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Lateral self‐assembly of E‐cadherin directed by cooperative calcium binding
Author(s) -
Alattia Jean-René,
Ames James B.,
Porumb Tudor,
Tong Kit I.,
Heng Yew Meng,
Ottensmeyer Peter,
Kay Cyril M.,
Ikura Mitsuhiko
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(97)01333-1
Subject(s) - cooperativity , dimer , chemistry , cooperative binding , sedimentation equilibrium , biophysics , crystallography , titration , calcium , binding constant , molecule , binding site , dynamic light scattering , sedimentation coefficient , fluorescence , biochemistry , enzyme , biology , nanotechnology , inorganic chemistry , materials science , physics , organic chemistry , quantum mechanics , nanoparticle
We report the Ca 2+ binding characteristics of recombinant Ecad12, a construct spanning the first two repeats of epithelial cadherin, and demonstrate the links between Ca 2+ binding and dimer formation. Sedimentation equilibrium and dynamic light scattering experiments show that weak dimerization of Ecad12 occurs in the presence of 10 mM Ca 2+ ( K P d =0.17 mM), while no appreciable dimer formation was detected in the absence of Ca 2+ . Ca 2+ ‐induced dimerization was also observed in electron microscopy images of Ecad12. We conclude from Ca 2+ titration experiments monitored by tryptophan fluorescence and flow dialysis that dimerization does not affect the equilibrium binding constant for Ca 2+ . However, the value of the Hill coefficient for Ca 2+ binding increases from 1.5 to 2.4 as the protein concentration increases, showing that dimer formation largely contributes to the cooperativity in Ca 2+ binding. Based on these observations and previous crystallographic studies, we propose that calcium acts more likely as a geometrical aligner ensuring the proper assembly of cadherin molecules, rather than a simple adhesive.